Q: I am a 53-year-old woman. I’m 5 feet, 6 inches tall and weigh 118 pounds. I walk or do step aerobics carrying 2- to 3-pound weights five days a week for one hour per day, and I do a weight routine with 5- to 10-pound weights every other day. A 68-year-old co-worker told me I’m going to wear out my body. Is this really too much exercise? I feel fantastic, and I'm not bragging, but most people think I'm in my 30s. I’ve been exercising for 30 years. But some people do tell me I over-exercise.

A: It doesn’t sound like you’re over-exercising, says Dr. W. Ben Kibler, a spokesperson for the American College of Sports Medicine and medical director of the Lexington Clinic Sports Medicine Center in Lexington, Ky.

“This volume of exercise probably is within the tolerance levels of the body, if there are no other factors, such as prior injury,” says Kibler. Just make sure you’re also getting at least two days of rest and recovery each week to avoid injury, he says.

Physical activity guidelines released by the federal government last year recommend a minimum of two hours and 30 minutes a week of moderate physical activity or at least one hour and 15 minutes of vigorous activity, plus at least two days of strength training a week. The guidelines also state that greater health benefits can be achieved when adults like yourself increase their physical activity to five hours a week of moderate activity or 2.5 hours of vigorous activity, or more.

Kibler commends you on sticking with a regular fitness routine for so many years, which can help keep the body strong and more resistant to injury. He also likes that you’re doing both aerobic and strength-training activities to round out your program.

But what about your co-worker’s comment that exercise can “wear out” the body? We get this question occasionally from readers who wonder if physical activity will inevitably wear us out like a rickety old train that’s rolled down its last track.

It’s true that you can overdo it with exercise and sustain overtraining injuries, particularly if you don’t follow good technique or listen to your body’s warning signals to taper off, Kibler and other experts say. But there’s no reason to think that healthy people doing recommended amounts of physical activity and progressing at a sensible rate are going to eventually wear out their bodies. On the contrary, there is abundant evidence that exercise can go a long way to keep us healthy and strong as we age — and prevent early death.

Still, there is a fairly common concern among exercisers that high-impact exercise such as running will eventually destroy the knees. But as Dr. Ron Noy, a New York City sports medicine specialist and spokesman for the American Academy of Orthopaedic Surgeons, points out, running helps the joints stay lubricated and healthy, and keeps the bones and heart strong.

“If you have a healthy knee, running is not going to damage the knee,” he says. “It’s not going to wear down your knee, and there are benefits to the joint from running.”

It’s a different story, though, if you have an arthritic or injured knee, which gives the body “less protective power” against high-impact activity, Noy says. Problems also can arise in obese people who are sedentary and then jump into a rigorous exercise program, which can overload a deconditioned body, he says, possibly leading to knee injuries, stress fractures or other problems.

So it would not be a good idea, for instance, for a 250-pound couch potato to start out running 12 miles a day, Noy says. “You have to acclimate your body to accept that load,” he says, with a “slow, progressive program.”

Even normal weight people with no health issues can become injured if they push too far, too fast in a range of activities. How much is too much varies from individual to individual, so as your program progresses, listen to your body, says Noy. If you’re getting signals such as pain, swelling or extreme fatigue, scale back. An experienced coach or personal trainer can help recreational athletes develop a safe program that incorporates proper technique and equipment.

And it’s always a good idea to get a checkup before starting a training program, Noy says. It’s especially important to identify any potential heart problems or risk factors such as a family history of early cardiac death that might lead to sudden death during exercise. Be sure to discuss with your doctor any chest pain, shortness of breath or prior difficulty exercising in hot temperatures.

Kibler points out that people who die during endurance exercise often have underlying health problems or they push themselves too hard in the heat.

“There’s usually some identifiable reason outside of exercise,” he says. “But exercise is the trigger.”

Q: I was told not to shower right after I work out. Does it make a difference how soon after you exercise that you take a shower?

A: “The street myth is that if you are hot and take a shower and get cooled down quickly, you can have a cardiac problem, and that is rare,” Kibler says.

People with underlying heart conditions could potentially experience a dangerous drop in blood pressure and maybe pass out or even have a heart attack or stroke if they were exercising in excessive heat, got their body temperature up to 104 or 105 degrees Fahrenheit — and then immediately jumped into an ice-cold shower, he says.

But that’s hardly a likely scenario. Most people don’t exercise that hard and they certainly don’t jump right into ice water afterward. At the very least, they cool off a bit while walking to the locker room or shower and undressing.

Bottom line, says Kibler, “This is no reason not to take a shower.”

Jacqueline Stenson is a freelance writer in Los Angeles. A former senior health producer for msnbc.com, her work also has appeared in publications including the Los Angeles Times, Health, Shape, Women’s Health, Fit Pregnancy and Reuters Health.

In a highly-anticipated speech to Congress Tuesday, Israeli Prime Minister Benjamin Netanyahu argued that a potential nuclear deal being negotiated by major powers including the United States "paves Iran's path to the bomb."